Laminated metal sprockets positioned on rotatable drive shafts for driving plastic modular belts are introduced in the related parent U.S. Pat. No. 5,074,406, Dec. 24, 1991 and U.S. Pat. No. 5,156,263, Oct. 20, 1992.
Operational experience with metal sprocket driving systems for plastic modular belts has indicated various unsolved problems pertinent to belt system operating life and reliability under dynamic operating conditions frequently encountered.
Because of the relatively flexible character of plastic modular conveyor belts, the belts tend to sag, expand and contract with temperature, and vary in response to aging and loading, as contrasted with the relative stability and firmness of metal sprockets located on metal drive shafts. For example, lateral movement of the belt during operation can cause frictional loading and corresponding undesirable interference and wear because of mismatches in registration of metal sprockets with corresponding belt drive surfaces. The probability that changes of dimension is non-uniform across the belt width gives further problems of producing reliable belt drive systems operable under changing and variable dynamic conditions. Thus, individual sprocket drive lamina generally behave differently across the width of the belt in the presence of curvature in belt drive systems, loading imbalances across the belt, and the influence of railings at the belt edges.
The softer plastic modules are subject to wear from the harder metal drive sprockets. To reduce wear induced from belt stops and starts, it is important to keep the weight and inertia of metal drive sprockets low particularly when encountering variable speed or stop and go operating conditions. Thus, operating life is extended by employment of light weight sprocket systems.
Conveyor belts come in many variations, depending upon loading, speeds, widths, adaption for curvature of conveyor paths, and the like. These factors not only affect the variations of belt dimensions and the wear as aforesaid, particularly where heavy drive forces are required for high belt loads, but also demand significant differences in drive sprocket configurations. Thus, heavier loaded belts in general require more sprocket laminations dispersed across the width of a belt, and possibly different numbers of laminations in different drive positions across the belt width. Therefore a belt sprocket drive system needs to be modularized and flexible in configuration to avoid the necessity to design and inventory a variety of seldom used drive systems adapted to different ranges of belt functions.
Another problem is encountered in initial registration of a laminar type metal sprocket drive system with belt drive surfaces across a conveyor belt width. The lamina must be critically spaced axially along the drive shaft to register with drive surface apertures dispersed over the width of the conveyor belt. Once registered, the sprocket lamina may be maintained laterally in registration by the mating belt drive surface structure when the sprocket lamina are freely axially movably positioned to float on the drive shaft. However, the initial manual assembly of a drive system is awkward and tedious, particularly with wide belts having several lamina critically spaced over the belt width in ganged relationship.
It is therefore an objective of this invention to provide improved conveyor belt metal sprocket drive systems resolving the foregoing problems.
Other objects, features and advantages of the invention will be found throughout the following description, drawings and claims.